This invention relates to an image reading apparatus that changes a relative position between a reading unit and a reading target to read an image line by line.
There are known image reading apparatuses, such as a flat-bed type image reading apparatus and an auto document feeder-type (ADF-type) image reading apparatus. In the flat-bed type image reading apparatus, a reading target (a document) remains in a stationary state, and a reading unit performs reading operation while being conveyed over the reading target to thereby read image information of the reading target. In the ADF-type image reading apparatus, a reading unit remains in a fixed state and reads image information of a reading target (a document) while the reading target is conveyed over the reading unit.
Another type of image reading apparatus includes, as a reading unit, a CCD line sensor having a plurality of light receiving elements (photo diodes) aligned along a line direction. In this type of image reading apparatus, pixel data is generated depending on electric charges accumulated in the respective light receiving elements, and pixel data for one line is arranged to generate line image data.
A pulse motor and a DC (Direct Current) motor are known conventional drive sources for conveying the reading unit. The pulse motor is commonly used due to easiness in position control and convenience in configuring a control system of the pulse motor. A pulse motor, however, has disadvantages that noise and power consumption during driving are larger than in a DC motor and that scanning speed during driving is slower than in a DC motor. Therefore, in these days, development of an image reading apparatus, in which a DC motor is employed as a driving source, is performed actively for the purpose of reducing noise and power consumption and improving speediness during driving.